This invention relates to Voice over Internet Protocol (VoIP) calls and more particularly to a call fallback scheme used when quality of service degrades on the VoIP call.
Voice signals are transmitted over a packet network by first formatting the voice signal data stream into multiple discrete packets. In a Voice Over Internet Protocol call, an originating voice gateway quantizes an input audio stream into packets that are placed onto a packet network and routed to a destination voice gateway. The destination voice gateway decodes the packets back into a continuous digital audio stream that resembles the input audio stream. A codec uses a compression/decompression algorithm on the quantized digital audio stream to reduce the communication bandwidth required for transmitting the audio packets over the network.
The Quality of Service (QoS) of VoIP calls can degrade due to congestion on the packet network or failure of network processing nodes in the packet network. Quality of service can include anything from call sound quality to the ability and responsiveness of the VoIP network in establishing new VoIP calls. IP network reliability has not been proven to be in the same class as a traditional switched Public Services Telephone Network (PSTN). For this reason, many customers request features that place VoIP calls back out on the traditional circuit switched network (hairpinning) when there is IP network congestion or an IP network failure.
Hairpinning calls over the PSTN has several problems. The first is that hairpinning is expensive. A primary reason customers are attracted to VoIP calls is the cost savings over the PSTN network. Rerouting calls over the PSTN network eliminates a portion of that savings. Hairpinning also increases the number of PSTN channels that must be maintained for each customer by a factor of two (in the case of complete VoIP network failure).
Hairpinning is only used at call setup time. Once a VoIP call has gone into the active state, there is no way to then reroute the call through the PSTN network and then synchronize the PSTN call with the VoIP call. Thus, if the QoS of the IP network degrades during a VoIP call, that entire VoIP call will exhibit the degraded quality. If a QoS problem is detected before a new VoIP call is established, that new call can be hairpinned over the PSTN network. However, the remainder of that call continues to be hairpinned over the PSTN network even if the QoS of IP network improves. Thus, the customer continues to be charged for the more expensive PSTN call even though the call could have been reestablished over the IP network with acceptable QoS.
Accordingly, a need remains for a more effective way to provide VoIP call fallback.